The present invention relates to xerographic copying apparatus or the like and more particularly to copying apparatus wherein various size copies can be reproduced from a single document or the same size copy can be reproduced from different size documents.
In the type of copying apparatus herein contemplated, light rays or images are reflected from successive portions of an original document which is supported on a transparent platen. The light rays are provided by an illumination source which together with a reflector or mirror is supported for movement relative to the document supported on the platen. As the mirror is moved past the document, the light rays reflected from the document impinge upon the mirror and, in turn, are reflected onto a mirror cluster from which they are directed through a lens and finally impinge on a fixed mirror which redirects the light rays onto a photosensitive material, commonly carried on a rotatable drum, the drum being adapted for movement in the same direction and at the same speed as the illumination source and first mirror mentioned above. In the foregoing manner, images of successive portions of the original document are flowed onto successive portions of the photosensitive drum to thereby produce a latent image of the document in accordance with well-known techniques. It is necessary in producing a copy of the document by the foregoing type of optical projection system to maintain constant the distances over which the light rays travel from the document to the lens and from the latter to the photosensitive drum or at least a constant ratio therebetween should be maintained. This can be accomplished by the provision of a stationary lens, and first and second mirror assemblies which direct the light rays from the document and which are movable with respect to one another, the second mirror assembly being moved at half the speed of the first mirror assembly whereby the document to lens distance is maintained constant. It will be appreciated that such a copying apparatus cannot reproduce copies of the original at more than one magnification ratio which is usually a one-to-one ratio.
One technique for enabling a copier apparatus to make copies at more than one magnification has been to provide the copier with a plurality of lenses having different magnifying powers, and to substitute one lens for another, according to the degree of magnification desired.
In other copying apparatus it is known to make copies of documents at different magnifications by moving a lens simultaneously with reflecting mirrors, the lens generally being moved a much smaller distance than the mirrors.
Still other copiers of the prior art have been provided with variable magnification means wherein an add lens is provided to compensate for the lens movement.
Still further copiers have been provided with combination cable, cam and cam followers and associated linkages for effecting repositioning of the lens and certain mirrors of the optical projection system. Similarly, chains and gear sets have been provided for such purposes.
All of the foregoing embodiments for providing a variable magnification copier fall short of being simple in construction, simple to operate and simultaneously provide precise adjustment of the lens and associated mirrors when changing from one magnification ratio to another.
Accordingly, it is the general object of this invention to provide an improved copying apparatus capable of making copies of documents at different magnifications.
It is another object of this invention to provide a copying apparatus permitting different magnifications which is simple in construction, easy to operate and yet provides for precise relative repositioning of optical components when moving the components to accommodate different magnifications.
Another object of this invention is to provide an optical projection system capable of precision adjustment of the half-rate mirror relative to the full rate mirror and the lens to compensate for nominal production variations in lens focal length.
Still another object of the invention is to provide a magnification charge mechanism cable of precision adjustment in the conjugate distances when charging magnification while maintaining stiffness in the system to prevent distortion during scanning.
Yet another object of this invention is to provide a cable and pulley arrangement for accomplishing conjugate length adjustment thereby avoiding the chordal noise inherent in chains and gear sets heretofore employed for such purpose.
Still yet another object of this invention is to provide a cable and pulley arrangement for driving a first optical projection component at a first speed and driving a second optical projection component at a second speed equal to half said first speed.